In some systems the neutral is also bonded to ground... winds up being electrically the same thing.
I apologize for that sloppy and incomplete statement!
I now see that it could easily be misunderstood. A necessary clarification here... any neutral to ground bonding will take place at the
source distribution panel or service entrance only! Never out at any receptacles or equipment connection boxes.
It is because you must never use the ground wire as one of your live conductors within your house (or equipment) wiring. The ground is there as a safety conductor only for the possibility of equipment or wiring short circuits. This ensures that the circuit breaker (or fuse) will interrupt the circuit at its source if a short or insulation failure occurs anywhere in the circuit. This does NOT mean that the neutral or white insulated conductor in the circuit is not common with the ground in the system. Ultimately it will be as previously stated except for the clarification about physical circuit design and that bonding must be at the source fuse or circuit breaker (service entrance only) in most cases. Electrical code requirements may have flip-flopped over time but at one time a neutral bonded to ground (in the distribution panel) was a standard requirement... the manufacturers do provide for this option within their breaker or fuse panels - standard. North America NEC. We bond neutral to ground in many of our genset wiring configurations - and also provide a solid grounding rod connection from earth to all chassis portions of the plants. Some exceptions do exist but this is the norm. Take another look at the schematic diagram in one of the prior posts... Neutral is common with earth ground.
For operator and personnel safety there can NEVER be an electrically live chassis or metal casing or conduit located anywhere in the system even if accidental or caused by insulation failure. Add to this the potential exposure to electrical discharge in the event of lightning strikes. The ground portion of the circuit is therefore of very high priority.
It is of significant importance that you always have your electrical system at least vetted and safety checked by a professional who knows your local code requirements. Electrical shock can easily be lethal and must never be treated as something of only a casual or passing concern.Proper grounding and neutral bonding can be a complex and convoluted topic... the finer details are outside the scope of my discussion here. See NEC...
Where is it NEC compliant to bond neutral and ground? The NEC prescribes two places. The first place that we find this bond is at the service entrance inside the main service panels. Why? Fault current at this point needs to come from the utility source.
The other place where the neutral and ground are required to be bonded is on the secondary side of what the NEC calls a "separately derived system." The most common separately derived system is a power transformer where the primary and secondary windings are galvanically isolated from one another. This describes the NEMA-type transformer widely used to distribute power inside all commercial buildings. The reason for this is simple safety. The NEC wants the transformer providing the electric current in its own distribution system
to be sole source for fault current in the event of a fault in that distribution system. Fault current that does not have a short, low impedance path will not open breakers immediately.
Our generators are technically treated as separate utility "sources" but when connected through a transfer switch with household wiring and grid utilities it is sometimes important to also switch the neutral to avoid a code violation caused by the Neutral/Ground bond that is commonly present in the generator itself. Not all transfer switch types have this specific feature and not all localities will enforce this rule in the exact same way.
dieselgman